DESCRIPTION: (provided by the applicant) The transition from drug use to drug addiction typically occurs between adolescence and young adulthood, highlighting the importance of this developmental period to identifying factors influencing the onset and course of substance dependence. The project's primary goal is to determine predictors of the transition from adolescent substance use to dependence in a sample of adolescents (age 12-18) who were recruited through the Pittsburgh Adolescent Alcohol Research Center from addictions treatment (n=385) and community sources (n=163) who have been assessed with an extensive battery of baseline measures. The proposed award will support collection and analysis of adult (age 25 plus/minus 1) substance use and psychosocial outcomes, complementing on-going 1-, 3-, and 5-year follow-ups of the sample. The project will address three objectives described in the RFA. First, changes in drug use patterns in the transition to addiction will be characterized using growth mixture modeling. We hypothesize that trajectory classes differing in drug dependence severity and chronicity (e.g., developmentally-limited and persistent) represent identifiable developmental phenotypes. Second, the influence of co-occurring psychopathology, particularly conduct disorder, major depression, and posttraumatic stress disorder, on drug addiction transitions will be examined. We will examine common and reciprocal influence hypotheses to explain high rates of comorbidity between substance use disorders and psychopathology. Third, behavioral, psychosocial, and environmental factors will be examined as predictors of the transition from drug use to addiction by examining influences on the course of adolescent-onset substance use and related problems through adulthood. Use of a previously ascertained and well characterized sample of clinical and community adolescents represents a cost-effective approach to the identification of developmental phenotypes of adolescent-onset substance users that has with significant implications for prevention, genetics, and addictions treatment research.